Far-field reconstruction from near-field data collected through a planar spiral scan: experimental evidences

This communication provides the experimental validation of an efficient probe compensated near-field – far-field (NF– FF) transformation technique with planar spiral scanning, which requires a nonredundant, i.e. minimum, number of NF measurements. Such a technique allows a significant measurement time saving due to both the reduced number of needed NF data and the use of continuous and synchronized movements of the positioning systems. It is based on a nonredundant sampling representation of the voltage measured by the probe, obtained by using the unified theory of spiral scannings for nonspherical antennas and adopting an oblate ellipsoid to model a quasi-planar antenna. By using such a modelling, instead of the spherical one, it is possible to significantly reduce the error related to the truncation of the scanning zone, since the NF data can be acquired on a spiral lying on a plane placed at a distance smaller than one half of the antenna maximum size. An optimal sampling interpolation expansion is applied to efficiently retrieve the NF data needed by the classical plane-rectangular NF–FF transformation from those collected along the spiral. Some experimental results, performed at the UNISA Antenna Characterization Lab and assessing the effectiveness of the technique, are reported.